A recent study published
in the journal Nature dispels the theory that much of the nitrogen in
U.S. ecosystems comes from natural sources. Scientists now argue that
nitrogen pollution from acid rain and agricultural fertilizers is altering
U.S. ecosystems. Previously, ecologists believed that inorganic nitrogen
has always been the dominant nutrient in all forests.

The authors of the
January 24th article in Nature compared the unpolluted ecosystems of South
America to those of the United States, and found that South American forests
have a preponderance of organic nitrogen. Lars Hedin, a coauthor of the
study and a professor of ecology and evolutionary biology at Princeton
University said, "We traveled in time by traveling to South America."

The study shows that
U.S. ecosystems were much different prior to the industrial revolution.
The two reasons the U.S. has nitrogen pollution are because of burning
fossil fuels and the mass production of fertilizers.

Nitrogen is a plant
nutrient that determines the health of ecosystems, from local waterways
to global climate. The findings of this study raises questions about our
understanding of global warming: When trees mature they remove carbon
dioxide from the air. Yet, the ability of trees to grow and absorb more
carbon depends on the availability of nitrogen. "If we don't get
the fundamental elements of the nitrogen cycle right, we can't answer
many other ecological questions," said Steve Perakis, the paper's
lead author.